Cat drinking a little more, and urinating slightly more often after surgery/antibiotics?

My oldest cat is almost 4 years old. Recently, I noticed a lump in his throat and took him to the vet's. The vet prescribed clavaseptin for a week, which he took, but fluid started to accumulate, making his throat look huge, so about three days later, I returned to the vet's. The vet thought the lump was too soft to be a tumor, and said it was likely an abscess. Sam had surgery the same day, and it turned out the vet was right - it WAS an abscess.

He sent Sam home with more clavaseptin tablets and some onsior tablets. Sam took those for about a week, then he was prescribed another course of clavaseptin (for five days) to "prevent" infection. A few days after, he started having difficulty urinating, so I took him to the E-vets; saw a different vet, and she thought he had some kind of bladder infection. She gave Sam some slightly stronger antibiotics and some more onsior tablets to take for 10 days. Well, to cut an already long story short, Sam's infection did indeed clear up, but now, a couple of weeks later, and after all these tablets, I've noticed my beautiful cat has started to drink water occasionally, whereas he drank only occasionally before. He also pees at least 2-3 times a day. 

I'm reluctant to go back to the vet's in case they try to give him more medication, but I wanted to ask - can a course of antibiotics lasting 4 weeks possibly damage the kidneys? Or maybe I'm just being paranoid? :S

For what it's worth, Sam only eats wet food pouches (Nature's menu, hi-life) and freeze dried treats (Thrive), and Holistic natural food (Lily's Kitchen) whenever I can afford it (I'm a student and I have six other cats so this is perhaps once every two weeks. )

Sorry for the long back story, and thank you to anyone who reads this. 

Ugh, just re-red this thread and realized it's riddled with inconsistencies. Should have gone to bed early last night :S

What I meant is, that Sam used to drink very rarely before but now he's drinking fairly often.

The question: can taking antibiotics for 4 weeks cause kidney damage in such a young cat?

It's possible, though really rare.  It's also really rare, but the Onsior can cause excessive thirst. 

If you are concerned, you can always take him in for a simple blood test to see if his kidneys are fully functional.  Better to find out early if they aren't, so you can start him on fluids, or whatever might be necessary.  Does he seem dehydrated to you (doing to skin tenting test)?  BTW, naturally he would be having more output, if he's drinking more...those two things go hand in hand.  The question of WHY he's drinking more is the real question.  Why not call one of the Vets who prescribed the Onsior and ask about the excessive thirst and see if it's normal this long AFTER taking it?

Thank you for reading and for taking the time to respond, I appreciate it! Sam isn't dehydrated, but I just noticed that he has loose stools, and could be drinking more to compensate for the lost fluids? He also has quite an increased appetite. I called the vet's office earlier and they said they could do a urinalysis and a blood test, but the results would take a little time to come back. I'm not sure what to do... 

I should probably add that the stronger antibiotic the other vet gave was called Marbocyl. I asked her if it was dangerous at the time she was prescribing it and she actually laughed -_-. She said it isn't at all, but that was when I noticed he started drinking a little more water. 

antibiotics can definitely cause some digestive issues, same with people.  That would explain the loose stools, but not necessarily the increased appetite.  But cats with kidney issues don't usually have increased appetites...it's usually quite the opposite, so I wouldn't think you are looking at kidney disease.  

For the loose stools, especially after long term antibiotics, I would suggest you give him some probiotics.  Just mix them into his food.  I give mine the same ones WE take, and give them 1/2 capsule in the morning and 1/2 in the evening.  We all take them everyday, just to maintain good gut flora

So, again, back to the drinking and eating more than usual.  I would say if this is truly out of the norm, a blood test is in order.  I don't think a urinalysis would be needed, but would do a blood test if I were you.  Could be his thyroid, could be diabetes, could be nothing

Mrsgreenjeens, thank you so much for replying once again. In times like this when we're feeling so stressed and worried it really helps to have people like you who put the mind at rest somewhat. I will try the probiotics as well as chicken breast, and pumpkin has worked well in the past too.  I think I'll also have a blood test done for him some time as well, just to be clear on things. Once again, thank you. Btw, the cats in your avatar are so gorgeous!! Hugs